Hey all, A couple of months ago purchased a 3LN-3. Lately it's started to run rather rough and sounds like it's missing in the low revs. I changed the plugs, checked the leads and cleaned the air filter with not much improvement. I had a suspicion that it may be due for a valve clearance check/adjustment but decided to give the carbies a good clean first anyway. I stripped down the carbies, cleaned them with carbie cleaner, removed the jets & blew them out with compressed air. Put it all back together, back on the bike and now I've run into a problem. The bike seems to start and idle smoother however just revving in neutral it won't rev over about 5k, it seems to just bog down and die unless I release the throttle again. I have found if I rev it to about 3k then apply the choke it'll rev all the way up to redline fine, but it won't idle with choke on. So it seems it's running lean an not getting enough fuel through right? I've tried the needles in positions 2,3 & 4 (currently back on 3 which is how it was originally set) and there doesn't seem to be much difference between them. I've got the idle mixture screws 3 turns out, they were originally on 2 turns & I've tried them on 2 again, not a huge difference that I can notice between them, 3 turns is probably a slightly smoother idle. There is a good supply of fuel getting to the carbies (full tank, gravity feed) and turning the fuel tap off and opening the drain screws lets quite a bit of petrol out of the carbs. I haven't checked the float heights yet but that's what I plan to do next as soon as I find some clear PVC pipe. I did pull the floats out when cleaning the carbies however was very careful with them and hopefully put them back in exactly the same so I'm not sure that's the problem either? Does anyone have any thoughts on this? Any advice would be greatly appreciated.
I'd also check for fitment of the carbs on the intake boots/rubbers. Any air getting in will cause many headaches. Float heights could be an issue, but problems would be lessened with the addition of a fuel pump (which was a factory component). From what I understand from others is that the fuel pumps on these bikes were removed instead of replaced because of considerable cost.
Thanks for the suggestions. Tonight I pulled the carbs apart again, recleaned and rechecked everything. I put it back together and the same problem is still occurring. I've also discovered the bike is still not even idling properly. The two cylinders to the right of the bike, particularly the far right cylinder are not firing all the time. If I give it some choke and rev it up they do appear to kick in. I think this problem existed somewhat before I touched the carbs but it's only made things worse and now choke needs to be applied before it'll rev over 5krpm and if I apply choke with low revs even when the engine is cold is just dies. Later today I'll do a compression check on the cylinders, if the valve clearances are out the compression will probably be down won't it? I think compression should be about 120-140 ? The carbs are fitting in the intake boots well and they are tightened up well so there shouldn't be any air leaks there. I did a quick check of the float heights and if anything they actually seem to be a bit high and letting a bit too much fuel in. So I'll adjust them down asap but I don't really think that's the problem? The throttle cables are on correctly The needles, tubes & other usual wearing parts of the carbies all seem to be in rather good condition. The bikes done nearly 40,000 so I'd say they must have been replaced at some stage. I should have also mentioned when I first stripped down the carbs I did a balance via the ball bearing method. So that's really the only setting on the carbs I've changed. Things were working better before this but certainly not perfect. Supposing some of the cylinders are more worn then others and the ball bearing balance actually put it out more is there any chance this could be part of the problem & would it be worth my while getting some vacuum gauges and balancing them properly?
If the heads have not been done that you no of then thats what i would be looking at. Im thinking of doing my 2nd head job and this time a cam chain as well at 40000km
Damn I think I just wrote the reply to this one on the other that is stopping at 10K rpm. Dunno too much coffee. Umm about 5K rpm is where the needle will be providing most of the fuel, do a check on those and make sure the clips are on, needles slide nice and freely and there vacuum in the sytem. Chances are you may have put one of the vacuum lines or incorrectly. I doubt any of tht is your problem and there is an electrical gremlin in the system. Have a look at hte exup, my head keeps saying I;ve seen this before and that the exhaust valve was the culpret.
Ok, well I've just done a compression test... The results: 150, 130, 130 and 70 <!-- s:cry: --><img src="{SMILIES_PATH}/icon_cry.gif" alt=":cry:" title="Crying or Very sad" /><!-- s:cry: --> I'll be getting a couple of quotes from bike shops tomorrow but I imagine this isn't going to be too cheap to fix due to the labour involved? any idea what I should expect to pay? I'm kind of tempted to have a go at it myself however I've never pulled the head of a 4 cylinder bike before so I'm not overly confident and would really need some guidance which seems to be rather lacking for these bikes (except for these great forums of course!). But hey, if I never try I'll never learn how. Can anyone help with any guidance or reference material or do you strongly recommend it's worth the labour charges and just leave it to the experts? I put a bit of oil down the cylinder with 70 and compression then went up to about 120. Now I've read that this usually means it's the rings. However I have been told by someone else that there's still a good chance the oil is helping to seal the valves and it still may just need a valve adjustment. Any opinions? I guess this compression issue is at least the cause of most of my problems although it does seem strange that things suddenly got worse after cleaning the carbs. I guess I'll get the cylinders fixed & compression back up to normal, then if there's another problem I'll have to deal with it then.
If you are doing the rings you might as well do the heads at the same time. That is if you pay for it then most fo the labor should all ready be done. I would think that you might be up for cam chain and tensioners as well with them ks on the bike.
Well now you know there is a problem somewhere start with the free stuff and check the valve clearances. They will either confirm you have valves not sealing and they need adjustment or your problems are bigger.
